1. Field of the Invention
This invention pertains in general to the field of expiratory valves of an anesthesia patient breathing circuit in an anesthetic breathing apparatus. More particularly, the invention relates to an anesthetic breathing apparatus having an expiratory valve providing control of expiratory flow and pressure during a mechanical ventilation operation mode and providing a pressure-limiting function during manual ventilation operating mode of the anesthesia system.
2. Description of the Prior Art
Anesthesia patient breathing circuits of anesthetic breathing apparatuses, such as anesthesia machines, are utilized to convey gases containing an anesthetic vapor to a patient to carry out a narcosis of the patient. An anesthesia machine having a respiratory anesthesia delivery system comprising such an anesthesia patient breathing circuit provides a mixture of such gases and vaporized anesthetic agents. This mixture is conveyed to the patient via the anesthesia machine's patient breathing circuit.
When patients are subjected to anesthesia, there is usually a transition from spontaneous breathing of the patient, via a phase of manually controlled ventilation when the patient is sedated into anesthesia, to mechanically controlled ventilation, and vice versa when the patient is awakened out of anesthesia. In addition, it is sometimes desired during mechanical ventilation that the operator wants to switch over to a phase of manually controlled ventilation in order to check the condition of the patient, for example in connection with a change in the composition of an anesthetic gas.
Anesthesia patient breathing circuits therefore usually provide manual ventilation as well as automatic mechanical ventilation system, and a ventilation selection switch for selecting between the manual and the mechanical ventilation mode.
In order to limit the maximum pressure during manual ventilation, an adjustable pressure limiting (APL) valve is provided in the anesthesia patient breathing circuit. The APL valve is a pressure relief valve that vents the anesthesia patient breathing circuit when the pressure within the circuit reaches a predetermined level, such that the patient is not subjected to an excessive pressure. The APL valve is adjustable by the user so that differing maximum pressures are allowed in the patient breathing system during an operation and can be determined by the user.
Conventionally, the APL valve is provided with a spring that exerts pressure on a diaphragm that seals off a vent passage against a valve seat. For instance U.S. Pat. No. 5,950,623 discloses such a mechanical APL valve. When the pressure exceeds the spring force, the APL valve opens to vent excess gas into an evacuation system. The valve is adjusted by compressing the spring with a screw mechanism so that the level of the compressed spring force corresponds to the wanted pressure limit.
Such a mechanical APL valve is normally operating independently of any electric power supply to the anesthesia machine. However, the function of such mechanical APL valves may be impaired by a disadvantageously low accuracy of the adjusted pressure limit, as well as an inertial delay during opening.
Furthermore, the mechanical construction of the valve operating unit is subject to wear and tear, which on the one hand limits the life of the operating unit, and which on the other hand leads to an undesired variation of the adjustment mechanism over time. In addition, APL valves of the type disclosed in U.S. Pat. No. 5,950,623 need to be sterilized between patients, e.g. by autoclaving the control knob and valve mechanism. This contributes to an accelerated wear of the APL valve mechanism. Moreover, such mechanical APL valves may be slow in operation. In addition, costs arise for unmounting and disassembling such mechanical APL valves for a necessary cleaning and/or disinfection, e.g. by autoclaving the APL valves, as well as a subsequent re-assembly of the APL valve parts and re-mounting into the anesthesia breathing apparatus.
Hence, APL valves are traditionally components in anesthesia breathing apparatuses, which are cause of a number of issues that need to be eliminated.
An electronic solution for controlling an APL valve is disclosed in EP-A1-1421966 of the same applicant as the present application.
In the unpublished patent application PCT/EP2006/070068 of the same applicant as the present application, which is incorporated herein by reference in its entirety, an electronically controlled APL valve is described. In particular, reference is made to FIG. 1 and FIG. 5 as well as the corresponding description of PCT/EP2006/070068 that illustrates and describes a ventilation system having an electronically controlled APL valve.
However, a drawback of such electronically controlled and operated APL valves is that these do not operate at power failure. These type of APL valves is superior to mechanical APL valves, but they are dependent on an electrical power supply, which may result in a potential safety issue at power failure.
DE29807005U1 discloses an adjustable pressure-relief gas valve that has a valve that is opened by an electromagnetic jack drive and that is pressed closed against a seat, wherein a closure force thereof is adjustable using a bi stable, mechanical, spring based adjustment mechanism. The valve can be moved between operation in an open ventilation position, and a closed position, in which the valve is pressed against a valve seat. The valve is opened by an electromagnetic jack drive with a connecting rod to adjust the operation position of the valve. The valve is intended for use with an anesthetic-control unit or a patient respiration unit, in order to change the operation mode of the unit between manually controlled and spontaneous patient respiration. The valve setting can be selected from a central control unit and displayed on a monitor. A manual function remains available for emergencies, e.g. power failures, facilitating change to manual operation. However, the valve has to be switched manually by means of a lever to the emergency mode and in this emergency mode the valve functions as a conventional mechanical, spring biased, pressure limiting valve with all the drawbacks thereof.
Thus, there is a need for an electronically controlled APL valve, which during power failure situations may be operated independently of an electrical power supply with a similarly advantageous mode of operation as an electronically controlled APL valve.
Hence, an improved electronically controlled valve providing an adjustable pressure limit, which during power failure situations may operate independently of an electrical power supply, would be advantageous. In particular such an electronically controlled valve allowing for increased patient safety by providing the possibility to both work electronically with high precision and which operates independently of a power supply at power failure situations, and which is sufficiently sensitive and fast in operation as an electrically controlled valve, would be advantageous.